A Eurobalise is a transponder placed between the rails of a railway. These balises constitute an integral part of the European Train Control System, where they serve as "beacons" giving the exact location of a train as well as transmitting signalling information in a digital telegram to the train.
The downlink uses an amplitude modulation on the 27.095 MHz frequency. This frequency is used to power the passive balises (it is the intermediate channel 11A in CB radio).
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